Yeah it is 1100Mhz ram that OCZ brought out.
You will need to set your ram voltage to 2.1volts in the bios to get these sticks to work mate. Your 6400 sticks of ram use 1.65 the default setting for that bios if I recall. So pop one stick of your old ram in, change the voltages in your bios. Save and exit. Replace with the new sticks and you are good to go.